TEHRAN, Iran 
Iran's constitutional watchdog rebuked the president Wednesday for trying to merge Cabinet ministries without parliamentary approval - the latest sign of discord at the highest levels of the ruling Islamic system in Tehran.

President Mahmoud Ahmadinejad has been locked in a simmering confrontation for weeks with Iran's highest authority, Supreme Leader Ayatollah Ali Khamenei. It appears to be part of a power struggle ahead of parliamentary elections next year and the vote for Ahmadinejad's successor in mid-2013.

The latest slap to Ahmadinejad came after he tried to streamline his government by combining eight ministries into four without seeking parliamentary approval.

The Guardian Council, which oversees government adherence to the constitution, rejected the move. Hard-line cleric Ayatollah Ahmad Jannati, leader of the Guardian Council, ruled that the new ministers would have to be submitted to the parliament for a vote of confidence.

Jannati supported parliamentary speaker Ali Larijani, a key Ahmadinejad foe from a rival camp within the president's conservative political bloc. Larijani and Jannati maintained that this required a vote of confidence from parliament - something Ahmadinejad has refused to submit to.

Jannati has long been considered a key backer of Ahmadinejad, and his siding with Larijani signaled that the president's support base is melting down after he challenged the all-encompassing authority of Khamenei.

The internal political disputes involve hard-liners on both sides locked in disputes over who should control the next parliament and government.

Larijani is leading conservatives in the parliament who have increasingly turned into strong critics of Ahmadinejad.

The latest troubles emerged last month when Khamenei vetoed Ahmadinejad's attempt to fire his intelligence minister, Heidar Moslehi, and take control of intelligence himself.

Although Ahmadinejad has publicly backed down in the confrontation with Khamenei, it has emboldened his hardline rivals in parliament to challenge him.

Ahmadinejad was re-elected president in 2009 in a hotly disputed election that deeply split the country.

With parliament reasserting itself against Ahmadinejad, it could summon the president for a round of embarrassing questioning and could even go so far as to start impeachment procedures.

Some Iranian news websites have reported that lawmakers have collected signatures to summon Ahmadinejad to parliament for questioning. If it happens, the move will make Ahmadinejad Iran's first president to be summoned for questioning since the Islamic Revolution 32 years ago.

At a Wednesday Cabinet meeting, Ahmadinejad hit back at his rival Larijani.

"The parliament speaker assumes he is the law. This is not correct. ... One can't interpret the law the way he wishes and impose it on the government," the president said, according to the official IRNA news agency.

"This is disrupting the administration of the country," Ahmadinejad said.

Hours later, Jannati wrote to Larijani saying the parliament was right and that the president was wrong about the Cabinet restructuring.

"Ministers in merged ministries are considered new ministers and are required to obtain a vote of confidence from the parliament," Jannati said.